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Genomics key to reducing cows’ carbon footprint (July/Aug '23)

Using genomic data and genetic tools to support breeding decisions can help to significantly – and quickly – reduce greenhouse gas emissions and carbon footprint of UK dairy herds.


Between 65% and 70% of a typical dairy herd’s total carbon footprint is attributed to cows’ enteric methane production and feed utilisation. That’s a significant figure. But the good news is that both these contributors can be influenced by genetics, and there are some big wins to be had, according to Kite Consulting’s vet and genetic specialist Rose Jackson. “Just a small improvement in herd genetics can have a big impact on a herd’s carbon footprint,” she told visitors to the recent Down to Earth South event, held at Neil Baker’s Somerset-based dairy unit, and organised by RABDF.

She explained that carbon footprint (CFP) reduction is primarily influenced through production efficiency gains and by driving down emissions per unit of output, and she highlighted a practical example of how this approach is helping one robotically-milked herd to achieve significant and realistic progress towards carbon-reduction goals.

“In 2022, this herd produced an average of 9,900kg milk, with the top cow yielding 15,600kg, and recorded a CFP of 1,004g/kg FPCM. But now, with a combination of genomic testing and utilising genetics from their top-performing cows, they are on track toachieving a herd average yield above 15,000kg by 2032. And spreading the herd’s CFP across those additional kilogrammes of milk reduces the figure to 663g/kg FPCM. That’s a 33% reduction in CFP through increased production alone, in just 10 years.”

Environmental credentials

This herd has recently been looking at EnviroCow, the first independent genetic index in the world focused solely on breeding cows for their environmental credentials. This index, which is highly correlated with PLI, helps producers to breed cows that have a longer lifespan with better production, fertility, and feed efficiency.

“These are all traits that producers want to improve in their dairy herds, but they also offer significant environmental ‘wins’,” said Ms Jackson. “They were chosen as metrics because they all influence dry matter intake, which is directly related to methane output. And looking specifically at methane emissions, AHDB data shows that that the top 10% of EnviroCow cows will produce 21% less methane than the bottom 10%.” The EnviroCow score is set on a scale of -3 to +3, with every point equivalent to an estimated 5.5% reduction of CFP based on phenotypic data, such as lifetime production and fertility. This reduction does not consider downstream savings in terms of land use or fertiliser, making it a conservative figure.

Feed Advantage, a separate index within EnviroCow, was developed from 30 years of research at the Dumfries-based Langhill herd. Dry matter intakes were measured for two distinct genetic lines using both high- and low-forage feeding systems to create a genomic index that effectively serves as a feed-efficiency score.

Genomic tools

Additional genomic tools have also been developed to help improve sustainability through better feed efficiency, health and fitness, and lower methane emissions. “The problem with looking at dry matter intake alone, in the case of Feed Advantage, is that it’s tied closely to other factors such as body size and milk production, making it difficult to select for,” explained Ms Jackson.

Cogent’s EcoFeed trait is a genomic estimation of residual feed intake, which is a measure of feed efficiency. Put simply, it’s the difference between what we would expect a cow to eat depending on factors including her size and stage of lactation, and what she actually eats.

“The top 10% of EcoFeed heifers eat 15% less than the bottom 10%, which results in a 15% reduction in methane production. This approach makes even more sense when you consider not only the carbon cost of feed, but also the feed’s direct financial cost,” she added.

Down to Earth South: visitors found out more about breeding tools to reduce emissions

Visitors to Down to Earth South were also reminded that the most profitable cows in the herd are those that are ‘trouble free’. “So selecting sires to breed healthy and long-life cows will also improve sustainability credentials. Not only does disease incur costs, such as labour and vet treatment, but it also reduces milk production and increases the risk of culling. CLARIFIDE Plus is a genomic test that allows producers to select for traits related to health and wellness.

Semex recently launched a methane-efficiency trait as part of its genomic package. Methane output varies from cow to cow and around 24% is influenced by the animal’s genetics.

“The good news is that methane output is not correlated to any other trait, because we don’t want to select for it and make everything else go awry,” said Ms Jackson. “Methane efficiency is also moderately heritable, at 23%, which means selection for the trait could result in relatively quick changes in a herd. As a comparison, fertility has 3% heritability while milk constituents are higher still at 60%.”

Semex’s Owain Harries, who also attended the event, added that selecting for methane is not a silver bullet to be used exclusively. “But it is one of several tools that can be utilised to reduce methane emissions. Just by excluding below-average cows from replacement breeding we could see a 10% reduction in methane emissions.

Methane-efficiency data

“To make progress for the future we need to take action and use this methane-efficiency data now, even if it’s not a breeding-programme priority. Irrespective of herd size, every UK dairy business has the potential to reduce their emissions using this tool without changing their key breeding goals,” Mr Harries says.

Genomic testing is a tool used by producer Neil Baker, who hosted this year’s Down to Earth South event at Rushywood Farm, to track his herd’s progress. He’s recently tested 200 of the herd’s 1,800 dairy heifers using Semex’s Elevate, which includes the methaneefficiency index, as well as EnviroCow.

During the past few years, he has been selecting for lifetime production rather than specific sustainability traits. But when different generations of the herd were tested, progress could be seen in sustainability traits due to that focus on production.

“The EnviroCow figures show that the top cows in the herd have a 30% lower CFP than those at the bottom – and that Mr Baker is well ahead of the game,” said Ms Jackson. “The average EnviroCow score for the UK is 0.3 for cows and 1.0 for youngstock, but his herd is in the top 5% of the UK for EnviroCow, with cows scoring 1.0 and youngstock at 2.3.”

Mr Baker’s herd also performs well on the PLI index and, again, is in the UK’s top 5%. “This further supports the idea that sustainability and productivity go hand in hand,” she adds, estimating that continued focus on this index will also further improve profitability. “One study found that every point on PLI results in an extra £1.58 per lactation, so using this herd’s £PLI scores, the difference between the top- and bottom-ranked animal is equivalent to more than £1,600 per lactation.”

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